Leaf-eating caterpillars can send 'voicemail' messages to future generations just by altering the plants they feast on. (Photo: Creative Commons)

Insects who want to warn off other bugs about dangerous poisons in plants or tell others to steer clear of their grub have been known to use plants as a kind of telephone. No electronics necessary here, though.

All it takes is for insects to eat the roots of the plant, which changes the chemical composition of the leaves and causes the plat to emit volatile signals into the air.

But now, Dutch researchers have found that bugs can take their 'phone tree' method a bit further. Herbivorous insects can leave a kind of 'voicemail' in the soil after they have fed on a plant. Future plants growing in the same soil can pick up that message and transmit it to insects it may encounter in the future. And the messages are pretty specific.

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The insects that feed on a plant's leaves or roots make a change in the soil fungus around that plant. When new plants grow in the same soil, they can tell if the previous plants were suffering from conditions harmful to insects and relay that to their new host of bugs.

"The new plants are actually decoding a 'voicemail' message from the past to the next generation of plant-feeding insects, and their enemies," said researcher and lead study author Olga Kostenko. "The insects are re-living the past."

The messages left not only affect the growth pattern of the plants, but the behavior of future bugs around those plants.

In an experiment, researchers grew ragwort plants in a greenhouse and exposed them to leaf-eating caterpillars or root-feeding beetle larvae. They then grew new plants in the same soil and exposed them to insects again.

"What we discovered is that the composition of fungi in the soil changed greatly and depended on whether the insect had been feeding on roots or leaves," said Kostenko. "These changes in fungal community, in turn, affected the growth and chemistry of the next batch of plants and therefore the insects on those plants."

Unlike our own voicemail messages which are deleted at the swipe of a key, these messages from the past can stick around through several new plantings.

"How long are these voicemail messages kept in the soil? That's what I also would like to know," said Kostenko, according to The Daily Mail. "We're working on this, and on the question of how widespread this phenomenon is in nature."